In recent years, the Sigma-Delta analog-to-digital converter is getting more and more attention due to its advantages such as high accuracy, high integration and low power consumption. There are two types of Sigma-Delta analog-to-digital converter, i.e., a continuous time type and a discrete time type, in view of the implementation of the integrator in the Sigma-Delta analog-to-digital converter. Compared with the discrete time Sigma-Delta analog-to-digital converter, the continuous time Sigma-Delta analog-to-digital converter has advantages of lower power consumption, higher speed and the inherent advantage of anti-aliasing. These advantages can efficiently extend the battery lifetime and decrease the complexity of the system, which are important to a portable wireless device. Therefore, the continuous time Sigma-Delta analog-to-digital converter is getting more and more attention recently. A Sigma-Delta modulator is a part of the Sigma-Delta analog-to-digital converter. The integrator is a basic and core module in the Sigma-Delta modulator. Two types of integrator, namely, a RC integrator and a Gm-C integrator are widely used in the Sigma-Delta modulator nowadays. The main advantage of the RC integrator compared with the Gm-C integrator is higher linearity and greater input signal amplitude. In addition, the characteristic of virtual ground of the RC integrator may allow the output of the feedback DAC to be connected to the virtual ground input end of the operational amplifier, so as to increase the linearity of the feedback DAC. Therefore, the RC integrator is more applicable to be applied in the case that requires high linearity and great swing of the input signal.
Because the resistance deviation due to processes is high, for example, 25%, the integral coefficient 1/RC of the RC integrator is deviated as the deviation of processes. The deviation of the integral coefficient may decrease the overall performance of the Sigma-Delta modulator, and even may disable the modulation function of the overall circuit or produce oscillations. Therefore, the resistance and (or) the capacitance should be corrected in designation to avoid the influence of the process deviation on the overall performance of the modulator.
In the conventional technology, the correction of the resistance in the RC integrator is mainly achieved by adding new components, which will increase loop delay, designation complexity, and further increase additional chip area, power consumption and cost.